This invention relates to improvements in wobble dado assemblies whereby adjustable means are provided for tilting a circular cutting blade at various angles with respect to an arbor so as to utilize the blade to cut grooves or slots of varying width depending upon the degree of inclination of the blade. More particularly, the invention relates to improvements in such assemblies of the type wherein inner plates having complementary inclined surfaces are fixedly mounted to either side of a plate-like circular blade and rotatably mounted between a set of arbor-mounted outer plates also having complementary inclined surfaces, the variable inclination of the blade with respect to the arbor being obtained by rotating the inner plates and blade relative to the outer plates. A typical adjustable wobble dado assembly of this type is shown for example in Sam U.S. Pat. No. 3,159,191.
Such adjustable wobble dado assemblies have in the past suffered from major problems of dynamic imbalance caused by the combination of high arbor speed, rotational imbalance caused by loose tolerances and other geometric features needed to facilitate operation of the adjustable inner and outer plate adjustment mechanism, and too much concentration of weight in the blade of the assembly. The resultant dynamic imbalance can cause severe vibration and chattering at higher arbor speeds, defeating smoothness of operation and impairing the maintenance of proper blade adjustment.
One universal feature of all such previous adjustable wobble dado assemblies is that the degree of inclination of the blade is adjusted by rotating the inner plates with respect to the outer plates about cylindrical hubs on the outer plats which extend along an axis tilted with respect to the arbor axis. The adjustable rotational movement of the inner plates about such an axis, which is tilted relative to the axis of rotation of the entire device on the arbor shaft, minimizes rather than maximizes rotational balance of the assembly at all adjustable positions and has been at least partially responsible for the dynamic imbalance and vibration referred to above. However it has previously been considered necessary that the adjustable rotation of the blade and inner plates relative to the outer plates be about a hub extending perpendicular to the complementary inclined inner surfaces of the outer plates, which are always tilted with respect to the arbor axis of rotation, since any other rotational movement would result in binding between the inner and outer plates.
It has also been a problem to maintain a close tolerance between the outside diameter of the outer plate hubs and the inside diameter of the circular bores of the inner plates into which the hubs are inserted so as to permit the inner plates to rotate relative to the outer plates. This is due to the fact that the inner and outer plates are intended to be easily manually rotatable with respect to one another to facilitate variable adjustment of the device by the user. In past practice, the hubs and circular bores have engaged one another throughout substantially the entire width of the inner plates, thereby resulting in a rather large bearing area between the hubs and circular bores. Attempting to maintain a close tolerance over such a large bearing area while at the same time ensuring easy manual rotation of the bores with respect to the hubs has been difficult from the point of view of economical machining. Accordingly a rather large tolerance has usually been provided, permitting the inner plates and blade to become axially decentered (by the amount of the tolerance) with respect to the arbor during adjustment, thereby causing further dynamic imbalance.
Accordingly a need exists for an adjustable wobble dado assembly of the type described which overcomes these problems and thereby provides improved dynamic balance.